THE LOCUST OR THE CRAYFISH. 69 



Where, in your scheme, would the following terms fit: 

 swimmerets, chela, walking appendages, mandible, maxilli- 

 peds, maxilla, antennule, antennas? 



Appendages 



Pre-oral < How many, and of what kinds? 



Mouth parts 

 Post-oral < 



What is your final judgment as to the total number of 

 segments in the animal? 



Compare the appendages throughout with those of the 

 grasshopper. Are they more, or less, differentiated 

 and specialized? 



6. Internal Anatomy. With strong-pointed scissors, cut through 

 the skeleton along each side of the back, the whole length of the 

 animal. Be careful not to cut deep enough to injure the organs 

 beneath. Remove the part of the shell between the cuts very 

 gradually, and cut the attachments in such a way as to leave all 

 the soft parts in place. Some of the epidermis, which produces 

 the shell, will probably be removed with it. Remove what is left 

 after noting its texture and color. 



Study the following structures : 



a. Muscles. Examine the harder masses of flesh in the abdomen 

 and forward. Tease out a small portion and examine it under the 

 microscope and see if it shows the structure of muscle (see Fig. 2 5) . 

 In what directions do these various muscle fibres run? Examine 

 closely and see where some of them are attached. What would be 

 the result on the parts of the body from their contracting ? How 

 many of such muscles do you find? After the other organs are 

 removed examine for still other muscles, if time will allow. How 

 is the abdomen bent downward? How is it straightened? Which 

 are the more powerful muscles? Find the muscles that work the 

 jaws (mandibles) ; those that work the chela. 



b. The Heart. Unless the circulatory system has been injected 

 with a colored mass, little can be seen except the heart. It lies 

 just beneath the carapace, well back in the thorax. What is its 



